Tangential Combustor

ABSTRACT

A combustion section for a gas turbine includes a casing defining a chamber, a plurality of combustor cans disposed in the casing and oriented in an annular pattern, and a plurality of transition pieces each coupled with one of the combustor cans. The transition pieces direct products of combustion from the combustor cans into contact with rotating buckets of the gas turbine. Each of the transition pieces is angled in two planes to effect turning of the products of combustion and to shorten the gas turbine.

BACKGROUND OF THE INVENTION

The invention relates to a gas turbine and, more particularly, to acombustion section for a gas turbine including structure for turning airflow into the turbine.

In operating a gas turbine, gas flow is exhausted from the combustor androuted by the transition duct to first stage vanes and blades (rotatingbuckets). As the gas flow is discharged from the outlet of thetransition duct, the flow passes the first stage vanes. The function ofthe first stage vanes is to accelerate and turn the flow in acircumferential direction so that the predominant flow direction of thegas flow leaving the trailing edges of the vanes is angled in thecircumferential or tangential direction relative to the longitudinaldirection. This turned flow thus has a longitudinal component and acircumferential component. The flow angle can be substantial, in therange of 40 degrees to 85 degrees measured from the longitudinal axis.By accelerating and angling the gas flow in the circumferentialdirection relative to the longitudinal direction, the resulting gas flowmore effectively imparts its energy to the first row blades, which inturn rotate the associated rotor assembly.

The use of first stage vanes to accelerate and turn the longitudinal gasflow in the circumferential direction presents several challenges. Thevanes and the associated vane support structure must have high strengthcharacteristics to withstand the forces generated in changing thedirection of hot, high pressure gas flow over a substantial angle in arelatively short distance. The temperature of the gas flow and the heatgenerated by this turning process also require a vane cooling system.The forces and heat involved can crack and otherwise damage the vanesand associated support structure. To address these various requirementsand operating conditions, the first stage vanes and the associatedsupport structure and cooling systems have developed into a complexsystem that can be expensive to manufacture, install, and, in the eventof damage, repair and replace.

First stage nozzles add approximately 1.5% total pressure drop, reducingthe total pressure ratio of the machine. Performance is closely tied topressure ratio. Another major draw on engine performance is parasiticflows. The minimum compressor mass flow in current state of the artair-cooled gas turbines represents a major reduction in overall turbineperformance. This air flow could be reduced or effectively eliminated by(1) much smaller wetted surface area of the turning/throttling vanes (ifturning/throttling vanes are required), (2) possible use of closedcircuit cooling of the transition piece vanes, and (3) possible use ofair that cools the vanes then passes through the combustor.

It would be desirable to accelerate and tangentially turn a gas flow forpresentation to a first stage blade array without the complications andrelated costs and damage risks associated with first stage vanes.

BRIEF DESCRIPTION OF THE INVENTION

In an exemplary embodiment, a combustion section is provided for a gasturbine including rotating buckets that are driven by products ofcombustion from the combustion section. The combustion section includesa casing defining a chamber, a plurality of combustor cans disposed inthe casing and oriented in an annular pattern, and a plurality oftransition pieces one each coupled with each of the combustor cans. Thetransition pieces direct the products of combustion from the combustorcans into contact with the rotating buckets. Each of the transitionpieces is angled in two planes to effect turning of the products ofcombustion and to shorten the gas turbine.

In another exemplary embodiment, the transition pieces of the combustionsection are angled tangentially relative to the annular pattern andaxially in a flow direction.

In yet another exemplary embodiment, a method of directing products ofcombustion into contact with rotating buckets of a gas turbine includesthe steps of orienting a plurality of combustor cans in an annularpattern in a combustor casing, providing a plurality of transitionpieces each one coupled with one of the combustor cans, and angling thetransition pieces tangentially relative to the axial flow direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional combustor;

FIG. 2 is an end view of the combustion section in a gas turbine of thedescribed embodiments;

FIG. 3 is a side view of the combustion section showing the axialorientation of the transition pieces;

FIG. 4 shows an embodiment with the transition pieces includingthrottling guides/vanes; and

FIG. 5 shows an embodiment with the transition pieces turned.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a typical combustor for a gas turbine, which includesa compressor, a plurality of combustors, and a turbine. The compressorpressurizes inlet air, which is then reverse flowed to the combustorwhere it is used to cool the combustor and to provide air to thecombustion process. The combustor 10 includes a liner 12 that defines acombustion zone and a transition piece 14 that connects the outlet endof the combustor with an inlet end of the turbine to deliver products ofcombustion to the turbine. The interface between the combustiontransition piece 14 and the turbine first stage nozzle requires the useof seals to reduce leakages into the gas path.

FIG. 2 is an end view of a combustion section 30 for the gas turbine.The combustion section 30 includes a casing 32 defining a chamber, and aplurality of combustor cans 34 disposed in the casing and oriented in anannular pattern as shown. A plurality of transition pieces 36, one eachcoupled with each of the combustor cans 34, serves to direct products ofcombustion from the combustor cans 34 into contact with rotating bucketsof the turbine. Each of the transition pieces 36 is angled in two planesto effect turning of the products of combustion and to shorten the gasturbine.

As shown in FIG. 2, the transition pieces 36 are angled tangentiallyrelative to the annular pattern of combustor cans 34 (in an X-Y plane,with the Z axis into the page in FIG. 2). Additionally, the transitionpieces are angled axially in a flow direction (i.e., toward the turbinebuckets) as shown in FIG. 3 (in the Y-Z plane, with the X axis into thepage in FIG. 3). The angles are determined to effect a proper angle ofincidence to extract work from the rotating buckets. These angles varyon turbine design.

This structure offers benefits to gas turbine performance andconfiguration. In particular, the flange-to-flange length can beshortened, the pressure loss across the first stage nozzle can bedrastically reduced, and the first stage nozzle cooling and leakageflows can be drastically reduced. Angling of the combustor in thetangential direction allows the combustor to provide all or a portion ofthe turning effect that is typically applied in the first stage nozzleof the turbine. As a consequence, much lower pressure drop will occur inthe process of turning the air flow into the first stage bucket.

In yet another alternative arrangement, with reference to FIG. 4, thetransition piece includes throttling vanes 38. The throttling vanes maybe formed by contouring the sides of the transition piece. Thethrottling vanes would further accelerate and straighten the flow tobring the air to ideal conditions to extract work in the first stagebucket.

More recent aerodynamic analysis has shown that the throttling vanes maynot be required. In an alternative construction, with reference to FIG.5, ends of the transition pieces 36 may be turned, possibly up to 30° ormore, to give the required overall turning.

Another big reduction in heat load occurs because there is higher heattransfer where turning is taking place. With limited or nocircumferential turning being done on the hot side (now done before thecombustion chamber), the result is lower heat transfer on the hot side.Turning the air while it is still cold is a significant advantage ofthis configuration.

Additionally, the turning/throttling vanes (if required) will have muchsmaller wetted surface area than current first stage nozzles. As aresult, less heat transfer will be required to keep them withinacceptable material temperatures. Moreover, by integrating the combustortransition piece and the first stage turning vanes, the opportunity touse air that eventually passes through the combustor to cool the nozzleis facilitated. Since the combustor transition piece will take the placeof the first stage nozzle, there will be no interference leakagesbetween these two pieces as in conventional designs.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A combustion section for a gas turbine including rotating bucketsthat are driven by products of combustion from the combustion section,the combustion section comprising: a casing defining a chamber; aplurality of combustor cans disposed in the casing and oriented in anannular pattern; and a plurality of transition pieces each one coupledwith one of the combustor cans and directing the products of combustionfrom the combustor cans into contact with the rotating buckets, whereinthe transition pieces are angled tangentially relative to an axial flowdirection.
 2. A combustion section according to claim 1, wherein all ofthe combustor cans and the transition pieces are correspondingly angledtangentially relative to the axial flow direction.
 3. A combustionsection according to claim 1, wherein the combustor cans and thetransition pieces are angled to effect a proper angle of incidence toextract work with the rotating buckets.
 4. A combustion sectionaccording to claim 1, wherein ends of the plurality of transition piecesare turned.
 5. A combustion section according to claim 4, wherein theends of the plurality of transition pieces are turned up to 30°.
 6. Acombustion section according to claim 1, wherein the plurality oftransition pieces comprise throttling vanes.
 7. A combustion sectionaccording to claim 6, wherein the throttling vanes are formed bycontouring sides of the transition pieces.
 8. A combustion section for agas turbine including rotating buckets that are driven by products ofcombustion from the combustion section, the combustion sectioncomprising: a casing defining a chamber; a plurality of combustor cansdisposed in the casing and oriented in an annular pattern; and aplurality of transition pieces each coupled with one of the combustorcans and directing the products of combustion form the combustor cansinto contact with the rotating buckets, wherein each of the transitionpieces is angled in two planes to effect turning of the products ofcombustion and to shorten the gas turbine.
 9. A combustion sectionaccording to claim 8, wherein the two planes comprise a circumferentialplane and a tangential plane.
 10. A method of directing products ofcombustion into contact with rotating buckets of a gas turbine, themethod comprising: orienting a plurality of combustor cans in an annularpattern in a combustor casing; providing a plurality of transitionpieces one each coupled with each of the combustor cans; and angling thetransition pieces tangentially relative an axial flow direction.
 11. Amethod according to claim 10, wherein all of the combustor cans and thetransition pieces are correspondingly angled tangentially relative tothe axial flow direction.
 12. A method according to claim 10, whereinthe angling step is practiced by angling the transition pieces to effecta proper angle of incidence to extract work with the rotating buckets.13. A method according to claim 10, further comprising flowing productsof combustion from the combustor cans through the transition pieces intocontact with the rotating buckets.
 14. A method according to claim 13,wherein the flowing step comprises turning the products of combustion ina tangential direction relative to the annular pattern and turning theproducts of combustion in an axial direction toward the rotatingbuckets.
 15. A method according to claim 14, wherein the angling stepcomprises integrating the transition pieces with respective turningvanes of the rotating buckets.